INTRODUCTION: Previous observations indicate that estradiol causes an early increase in the translational efficiency of uterine ribosomes and that activation of the estrogen receptor in the uterine cytosol by estradiol may directly activate the peptide elongation process of the ribosomes. OBJECTIVE: 1) To determine the hormone specificity, dose requirements, physiology and time course of the estrogen induced increase in the peptide elongation rate by uterine ribosomes, 2) To determine the nature of an inhibitor of the peptide elongation process and the relationship between activation of the cytosol estrogen receptor by estradiol and the reversal of the action of the inhibitor, 3) To determine the specific reaction in the peptide elongation process which is stimulated by estradiol, and 4) To compare the ribosomal protein composition of ribosomes from control and estradiol treated rats to determine whether the presence or absence of a specific protein on the ribosomes is related to the response. METHODS: The peptide elongation rate by isolated uterine ribosomes will be measured by dividing the rate of 3H-leucine incorporation into protein/100 micrograms rRNA by the number of nascent peptides capable of being elongated as determined by the amount of 3H-puromycin incorporated into peptidyl-3H-puromycin/100 micrograms rRNA. Cytosol estrogen receptor will be measured by the 3H-estradiol exchange assay. Individual peptide elongation reactions and their components including elongation factors, will be measured by standard published procedure. Ribosomal protein composition will be determined by 2-dimensional polyacrylamide gel electrophoresis. SIGNIFICANCE: Activation of the translational capacity of preexisting uterine ribosomes simultaneously with the synthesis of "early mRNA's" may increase the rate of synthesis of uterine proteins which may have a unique regulatory function during early estrogen action in the uterus.